The perception of speech and language requires normal functioning of the auditory cortex. Abnormal brain function, due to alterations in wiring, i thought to be responsible for many disorders such as cerebral palsy, schizophrenia, autism, and tinnitus. Correction of these disorders would seem to require the ability to rewire the brain. The young brain can adjust its connectivity depending on external inputs especially during early critical periods. For example early experience with speech is required for the normal development of the brain, and abnormal experience prevents normal development. Replacement of sensory experience after the critical period does not lead to successful functional recovery. We are investigating the ability of the young cortex to establish and adjust its wiring in response to experience. We characterizing circuits throughout development, and identify and manipulate key neuronal populations that regulate development and plasticity. Our work focuses on the auditory cortex a region crucial for human language communication. The developing cerebral cortex contains an enigmatic population of neurons called subplate neurons. Remarkably, these neurons are largely absent in adults highlighting their specialized role in development. However, despite their importance, detailed knowledge about subplate neurons and their role(s) are sparse. We hypothesize that subplate neurons provide both a substrate to establish a template of intra-cortical organization and that early spontaneous activity and sensory experience shape the functional and synaptic organization of subplate. To address these fundamentally important issues we propose a series of in vivo and in vitro experiments in mouse auditory cortex using a combination of electrophysiological and imaging techniques. 1) What is the functional organization of the distinct subcircuits within subplate? 2) What is the role of subplate and early sensory activity in patterning of intra-cortical circuits? 3 What is the role of subplate and early sensory activity in sculpting the functional organization of auditory cortex? Collectively these experiments will provide the fundamental framework of understanding development and plasticity of auditory cortex by elucidating the function of a previously ignored central component of auditory cortex development.